1. Field of the Invention
The present invention relates to an image storage device for recording images through the use of a solid-state image sensor.
2. Description of the Prior Art
In conventional image storage devices employing a solid-state image sensor, a image signal obtained with the solid-state image sensor is once recorded on a magnetic tape, disc, drum or like magnetic recording medium. The image signal thus recorded is then transferred to a separate playback unit, from which it is applied to a TV receiver set or printer to produce thereon a visible image. It is important to arrange such an image storage device so that an image of a subject may be monitored during the image pickup operation or immediately thereafter. With such an arrangement, it is possible to check the image for a defect and to process each picture element data for improving its picture quality and other purposes as required.
In Japanese Published Unexamined Patent Application No. 136325/79 there is disclosed an image storage device which is capable of electronically recording an image of a subject and providing a visible display of the image on a visual display unit forming a part of the image storage device as well as recording the image on a recording medium.
FIG. 1 is a block diagram showing, by way of example, such a conventional image storage device provided with a visual display unit. The image storage device comprises a photoelectric converter 100 for receiving an optical input through an optical system, an A-D converter 101 for converting information from each picture element cell of the photoelectric conversion unit 100 into digital form, a buffer memory 102 for temporarily storing the digital signal, a D-A converter 103 for converting the digital signal from the buffer memory 102 into an analog signal, a visual display CTR 104 for receiving the analog image signal from the D-A converter 103 to visualize an image of a subject, a magnetic recorder 105 for recording the analog image signal from the D-A converter 103, and an exposure-readout controller 106 for regulating and controlling the abovesaid parts.
In FIG. 1, the photoelectric converter 100 is formed by CCD's, BBD's or the like and since they are of the destructive readout type, information of each picture element cell is once stored via the A-D converter 101 in the buffer memory 102 which is provided with storage areas having one-to-one correspondence to the picture element cells of the photoelectric converter 100. The buffer memory 102 is a circulating memory, which repeatedly sends out picture signals to the visual display CRT 104 via the D-A converter 103 and supplies picture information of one frame or cycle to the magnetic recorder 105.
As will be seen from the above, it is impossible in the prior art example to provide on the visual display unit a visual display of the image signal from the solid-state image sensor and to record it on the recording medium unless after the image signal is once loaded in an external large capacity buffer memory. Accordingly, the conventional image storage device requires a buffer memory of the capacity corresponding to the picture element cells and an A-D converter for loading signals in the buffer memory, and hence it has the defect of markedly complex circuit arrangement.
In addition, since the abovesaid prior art example is arranged so that a signal of the same speed as the image signal supplied to the visual display CRT 104 is also applied to the magnetic recorder 105, a highspeed magnetic recording system is required which has a sufficient accuracy for video-speed recording and magnetic recording is impossible with the use of, for example, an audio-grade magnetic recording mechanism.